Spider mites difficult to manage

Jack Bacheler North Carolina Extension Entomologist | Jun 21, 2006

Spider mites have historically been a minor problem in North Carolina in terms of overall acres treated during the past decade, with North Carolina producers treating only 1.3 percent of the cotton acreage averaged over the past four years.

Although present at damaging levels on a low percentage of our acreage, spider mites can be a difficult pest to manage for the producers unfortunate enough to have economic levels.

Mite treatments often result in the use of high rates of expensive materials that often provide mediocre results, particularly with a building population under hot, dry conditions.

Of more concern, however, may be a possible trend toward higher spider mite problems associated with the increased use of seed treatments followed by the almost inevitable foliar application(s) for thrips.

In a 2003-2004 survey of all of North Carolina's licensed crop consultants, the cotton acreage was divided into two groups — producers with the highest Temik use (100 percent of this group used Temik 15G at planting, typically 5 pound of product per acre) and those with the lowest Temik use (25 percent of this group used Temik and the remaining 75 percent used a seed treatment — either Gaucho, Gaucho Grande, or Cruiser).

This survey represented approximately 100 cotton producers each year. The consultants with producers who had more even splits of Temik vs. seed treatments used were not included in the survey.

Of the high Temik users, 0.58 percent of their acreage was treated for spider mites, while the high seed treatment group treated an average of 5.3 percent of their cotton acreage for mites. This translates into a whopping 9-fold higher incidence of spraying by producers opting for the seed treatment plus a foliar (in most cases Orthene) spray.

It would appear that the combination of a seed treatment with limited or no spider mite activity, followed by a product such as Orthene which can exacerbate mite problems, increases the odds of having to treat for mites greatly compared with Temik, which shows good miticidal activity and which tends to be sprayed less for thrips compared to the seed treatments.

With the almost unprecedented levels of foliar applications for thrips this season, following both Temik and the seed treatments, it will be interesting to see where and to what extent mite problems develop in 2006.

On the positive side, even though the odds of treating for spider mites following a seed treatment were almost 10-fold higher than with Temik in the survey, the odds of this acreage being treated were only about 1 in 20.

Although mite problems may not materialize in 2006, several factors suggest that this could be a banner year for mites:

Seed treatment use (Gaucho, Gaucho Grande, Avicta, and Cruiser) in North Carolina has never been higher,

Poor early growing conditions and high thrips levels have resulted in almost unprecedented foliar sprays for thrips.

This recent span of very hot dry weather may help push mite levels higher.

With plant bugs typically not a significant economic problem prior to bloom in North Carolina, our cotton producers often get a bit of an insect break between the end of the “thrips season” and the beginning of stink bug and/or bollworm concerns. This would appear to be a good year to check cotton fields for symptoms of spider mite damage, most often recognized initially by yellowish leaf speckling, followed by bronzing or a purplish color, and finally the dropping of yellowing leaves.

A hand lens is almost indispensable in looking for spider mites and their eggs on the inner mid veins on the underside of speckled or purplish leaves.

As opposed to past years in which mite levels and their symptoms primarily showed up in cotton field edges and proceeded inward, in 2004 and in 2005 it was also common for mites to show up initially throughout cotton fields, particularly in reduced-tillage situations.

Hopefully, mites will give us a break in 2006. However, that gift would surprise some of us.